One possible type of such an illumination module is described in published U.S. patent application No. 2001/045573, for example. This involves a light emitting diode chip being fixed on a leadframe and surrounded by a housing, so that the light coupling-out areas of the light emitting diode chip adjoin a gaseous atmosphere. Such a design affords the possibility, in particular, of using housing materials which do not experience aging under the influence of UV radiation and/or whose coefficient of thermal expansion is adapted to that of the leadframe. One disadvantage of such a semiconductor component is that electromagnetic radiation of the light emitting diode chip is coupled out directly toward air or toward a gas. On account of the generally relatively high refractive index of semiconductor materials, a large part of the light intensity is lost in this case as a result of internal reflection, in particular as a result of more frustrated total interval reflection (“frustrated reflection”) at the semiconductor/gas atmosphere interface. Since housings of this type, for protecting the light emitting diode chip, generally also have a covering, a further part of the light intensity is lost as a result of reflections at interfaces of said covering.
In order to achieve an improved coupling-out of light, light emitting diode chips are generally encapsulated with a light-transmissive potting or encapsulating material having a highest possible refractive index in such a way that, in particular, all light coupling-out areas of the light emitting diode chip are covered with said material. One example of such a component is described in Möllmer/Waitl, “Siemens SMT-TOPLED für die Oberflächenmontage” [Siemens SMT-TOPLED for surface mounting], Part 1: Properties and special features (Siemens Components 29 (1991), issue 4). Such a so-called TOPLED has a surface-mountable housing. The potting or encapsulating material that envelops the light emitting diode chip is generally an epoxy resin, which has an essentially planar coupling-out area in the case of a TOPLED. By virtue of its relatively high refractive index with respect to air, the epoxy resin effects an improved coupling-out of light from the light emitting diode chip and thus also an overall improved coupling-out of light to the surroundings. In addition, the coupling-out area of the potting or encapsulating material may have the form of a lens, whereby the light coupling-out efficiency is increased further. As an alternative, a separate lens may be applied to the potting or encapsulating material in the emission direction of the component.
One disadvantage of these designs is that, with the use of light emitting diode chips having a relatively short emission wavelength, in particular in the case of light emitting diode chips that emit in the UV range, they experience severe degradation on account of aging of the potting or encapsulating material having a high refractive index as a result of the electromagnetic radiation emitted by the light emitting diode chip. A further disadvantage is that such potting or encapsulating materials have greatly different coefficients of thermal expansion compared with semiconductor materials of light emitting diode chips, thus resulting in a limitation of the quantity of material and hence a limitation of the size of the component. Moreover, encapsulating light emitting diode chips with potting or encapsulating material is relatively expensive and can make up almost 50% of the total production costs for example in the case of a TOPLED.